Grinwoody is the head slave/majordomo of Andross Guile and his right-hand man. He is also, it is later revealed, the Old Man Of The Desert, leader of the Order Of The Broken Eye. Lastly, it is revealed at the end of The Broken Eye that he is the uncle of Harrdun, Hanishu, and Harraru - Ironfist, Tremblefist, and the Nuqaba, respectively.
He is tiny, clean-shaven, and has very dark skin, even for a Parian.
A native Parian, Grinwoody was a legalist before he was captured by Ilytian pirates, enslaved, and eventually sold to Andross. He is described as brilliant and discreet, which is why he had served as Andross' right-hand-man for 20 years at the beginning of the series.
Despite being described as "barely a drafter," Grinwoody trained to be a Blackguard after Andross pulled strings to get him in, where he made friends, learned secrets, and gained all of the Blackguards' drafting and combat training, then signed on with Andross the day he was to take his oath, an offense the Blackguards have not forgotten.